LG GX300
A 23 hour talk time and 20.3 days of stand-by time. In addition, LG GX300 provides a 2 megapixel camera with video recording, dual-SIM capability, FM radio, MP4 player and GPRS connectivity. GX300 has a 30MB internal memory and can be expandable to 4 GB through a microSD card. Most notable feature of GX300 is its active noise cancellation with dedicated mic.
Zen M25
Talk time of 16 hours and standby time of 72 days, probably the longest running standby time for a mobile phone. This can be useful as a secondary phone if you are using a power sucking smartphone. M25 is a dual-SIM phone which has video playing capability, 1.3 megapixel camera, FM Radio and loud speaker
Micromax X1i+
As a part of Micromax’s marathon battery series, X1i+ offers an 30 day battery back up and 15 hours of talk time. That could get you past a week without charging even if you are a heavy talker. In addition to the incredible talk time, XLi has a FM player, music player, theft tracker and the memory can be expanded to 2GB. Like all Micromaxies, this is a dual SIM phone.
Micromax X2i+
X2i+ offers 20 day standby time and 14 hour talk time. It’s is a dual SIM phone with FM player, music player and expandable memory of 4GB. Unlike X1i+, X2i+ has a digital camera. That is where it loses an hour of talk time. The only difference between X1i+ and X2i+ is the presence of camera and an extra 2GB readability on X2i+
Sony Ericsson J105 Naite
J105 provides a talk time of 13.75 hours and a standby time of 25 days. Battery life isn’t the only exciting feature of this phone. It packs in a 2 megapixel camera with video shooting capability and is 3G capable. The talk time and standby time provided are for 2G network though. On 3G the talk time comes down to 4 hours and 3o minutes. J105 comes with a 2 GB microSD card but can read a 8GB card. It has Bluetooth and USB connectivity. no Wi-Fi.
Nokia X2
X2 provides a 13.5 hours of talk time and 22.5 days of standby time. This baby comes with a 5 megapixel camera and a 2.2 inch screen. X2 can record videos in QVGA up to 20 fps. Dual speakers, FM radio, Bluetooth and USB make X2 a noteworthy phone. X2 can read up to 16 GB cards which has to be bought separately.
Samsung Guru Dual 25 E1225
Guru Dual 25 offers a 9 hours of talk time and 17.5 days of standby time. This just scraped through. In other words, I squeezed this in. If not this list would be dominated by Micromax. And we all hate monopoly don’t we? Samsung Guru Dual is a dual SIM phone from Samsung and has a FM Radio. That’s about it. A standard phone with dual SIM and good battery life.

Have you ever felt your cell phone vibrate and pulled it out of your pocket, expecting to to see a text or e-mail message, only to see a low-battery warning instead? Surely, you've uttered the dreaded words, "My phone is dying, so I have to say this fast!"
It may be time to consider investing in a phone with better battery life.
I don’t know about you, but the idea of carrying an extra battery or charger around, or even strapping a battery case to my phone is not all that appealing. But I’m realistic. Smartphones, with their big touch screens and fast processors, suck up a lot of power, so I’m not expecting to make it through the week on a single charge. Still, there’s no excuse for not being able to make it through the day.
For every phone we review here at PCMag we test continuous talk time, to measure just how much chatting you can do between charges. Although talk time doesn’t account for all the other ways we use our phones throughout the day, it’s still a useful indication of how long you can expect your battery to last. For most smartphones running on a 3G network, the average talk time is a little over six hours, which isn't bad. There are also a good number of phones that fall in the seven-hour range, which is even better.
But for this list, we’re rounding up phones that delivered at least eight hours of talk time—some go well beyond that—which should be more than enough juice to get you from morning to evening without a charge.

It is not at all defined that certain mobile has long battery life. It all depends on the applications running on mobile and its usage. Also you can find the mobile with longer battery by checking the specification marked on battery in terms of mAh i.e., Milliamp Hour in Li-ion battery. till now i had seen samsung galaxy note 2 with highest battery backup with Li-Ion 3100 mAh.